The present invention is directed to energy transfer between airstreams of a building and to recovery of heat energy being exhausted from a building. Particularly, the energy is recovered from or transferred to the exhaust of a bathroom system, and is preferably recovered in conjunction with the recovery of or transfer to energy from the building's return air stream.
Typical commercial buildings have minimum outside air ventilation requirements. Air handlers that are used in these buildings supply the building with air that is a mix of recirculated air and the required outside air. Such systems are sold by The Trane Company, a Division of American Standard Inc. under the trademarks Modular Climate Changer™ and may also be known in the industry as central station air handlers.
Schools and commercial buildings have two main sources of exhaust air: bathroom exhaust and system exhaust. The system exhaust is taken from the same air path as from the return airstream. The bathroom exhaust airflow amounts are dictated by local building codes. System exhaust airflows are the additional amount of air that must be removed from the building to keep the building from becoming overpressurized from the incoming outside ventilation air. To minimize the heating and cooling loads from the introduction of this outside air, energy can be recovered from the exhaust air by using and air-to-air heat exchanger such as an energy recovery wheel or an air-to-air plate heat exchanger.
A problem arises because previous energy recovery units recover energy from the system exhaust stream only. In part, this occurs because bathroom exhaust is an isolated airstream which is physically distinct from the supply air and return air streams providing air conditioning to the building. The end result is that a large percentage of energy is not recovered from a building exhaust airstream, because the bathroom exhaust airstream is ignored.
Also, the ratio of exhaust air to outside air is not optimal for the energy recovery device. This increases the payback time incurred from the cost of adding a heat recovery wheel or an air-to-air plate heat exchanger and adding an energy recovery function. This smaller ratio of exhaust air to outside air also increases the likelihood of frosting the energy recovery device during seasonal cold weather.